Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, and is suitable for an image pickup optical system included in an image pickup apparatus, such as a digital camera, a video camera, a television camera, a monitoring camera, or a camera for silver halide film.
Description of the Related Art
An image pickup optical system included in an image pickup apparatus is required to have a wide angle of view, a small size in terms of the entire system, and a high resolution. Furthermore, the focus unit is required to have a small size and lightweight, and a small variation in optical characteristics during focusing.
Conventionally, an inner-focus zoom lens where a lens unit having a negative refractive power is arranged on the most object side has been known as a zoom lens that satisfies these requirements.
Japanese Patent Application Laid-Open No. 2005-106878 discloses a zoom lens which consists of, in order from the object side to the image side: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; a third lens unit having a positive refractive power; and a fourth lens unit having a positive or negative refractive power, the zoom lens performing zooming by changing the intervals between the lens units. The zoom lens of Japanese Patent Application Laid-Open No. 2005-106878 performs focusing by moving a certain or some lens sections in the first lens unit. Japanese Patent Application Laid-Open No. 2007-94174 discloses a zoom lens which consists of, in order from the object side to the image side: a first lens unit having a negative refractive power; and a second lens unit having a positive refractive power, the zoom lens performing zooming by changing the interval between the lens units. The zoom lens of Japanese Patent Application Laid-Open No. 2007-94174 performs focusing by moving a certain or some lens sections of the second lens unit.
Japanese Patent Application Laid-Open No. 2009-169051 discloses a zoom lens which consists of, in order from the object side to the image side, a first to fourth lens units having negative, positive, negative and positive refractive powers, respectively, the zoom lens performing zooming by changing the intervals between the lens units. The zoom lens of Japanese Patent Application Laid-Open No. 2009-169051 performs focusing by moving a certain or some lens sections of the first lens unit and a certain or some lens sections of the third lens unit.
To achieve a wide angle of view while securing a predetermined zoom ratio and to achieve fine optical characteristics over the entire zoom range and the entire object distance range in a zoom lens, appropriate configuration of elements that constitute the zoom lens is important. The negative-lead zoom lens described above is asymmetric in terms of the entire lens system. Consequently, if focusing is performed by moving a certain or some lens sections of the lens system in the optical axis direction, variation in aberration tends to increase and the optical characteristics tend to be degraded.
Consequently, to achieve fine optical characteristics over the entire zoom range and the entire object distance range in the negative-lead zoom lens, appropriate setting of a zoom type (the number of lens units and the refractive power of each lens unit), selection of a lens section for focusing, and configuration of lenses is important. In particular, in the case of adopting a floating type that moves multiple lens sections during focusing to reduce variation in aberration during focusing, appropriate selection of multiple lens sections is important.